I previously posted a question about utilizing low-recoverable oil by placing gas turbine at subterranean location closer to oil field and supplying the electricity. But no case studies and feasibility studies done on it. I refined my idea into a context that makes it more feasible. Let's say underwater city like "Ocean Spiral" by Shimizu Corporation becomes a reality, If the underwater city is located near a deepwater oil reservoir with low-recovery potential, would it be able to extract these sources as fuel source (since it requires less pressure for them to recover the oil)? And since underwater pressure can also reach 1 kbar, can underwater city be incorporated with a chemical refinery that produces polyethylene (if they are located near natural gas fields)? The ethane can be cracked to feed into the reactor because the city itself is at atmospheric while the polyethylene reactor that require 100 bar can utilize pressure of the deep sea. And one last thing, since any combustion process produces carbon dioxide, can Sabatier reaction be done (utilizing hydrogen from cracking process) which also takes place about 10 bar? Any thoughts on this system??